A liquid crystal display employing a so-called active matrix substrate is known. The active matrix substrate comprises a substrate, on which a plurality of gate wires intersecting with a plurality of data wires and pixel driving elements are provided.
FIG. 5 shows a schematic structure of a conventional active matrix substrate, which includes a transparent dielectric substrate 30 made of glass or the like. A gate wire group 31 having a plurality of gate wires 31a's and a data wire group 32 having a plurality of data wires 32a's are provided on the dielectric substrate 30 in such a manner that the gate wires 31a's intersect with the data wires 32a's. A display area 33 (encircled by a two-dot chain line) is formed at the center of the dielectric substrate 30 in such a manner to include all the pixel driving elements provided individually at the intersections of the gate wires 31a's and data wires 32a's.
The structure of the display area 33 will be detailed with reference to FIGS. 3(a) and 3(b) of the present invention. FIG. 3(a) is a plan view of a pixel TFT 24, namely, a pixel driving element of one pixel portion. FIG. 3(b) is a cross section taken on line III(b) III(b) of FIG. 3 (a) . The pixel TFT 24 is made in the following manner. To begin with, a gate wire 1a made of a Ta (tantalum) thin film or the like is formed on a dielectric substrate 8. Then, a gate insulating film 9 is layered on the dielectric substrate 8, and atop of which an amorphous silicon layer 10 that will be made into a TFT activating layer is formed. Subsequently, the amorphous silicon layer 10 is subject to patterning. Next, a pixel electrode 11 is made out of an ITO (Indium Tin Oxide) film in a region adjacent to the one where the pixel TFT 24 will be formed. Then, a Ta thin film or the like is layered, and a data wire 2a, a source electrode 12, and a drain electrode 13 are made through patterning in such a manner to be connected to the pixel TFT 24.
Incidentally, while assembling a display device, static electricity generated by handling or the like often causes element damages in the active matrix substrate, such as damages to the pixel TFT or the insulating film at the intersections of the gate wires 31a's and data wires 32a's. Thus, it is important for the active matrix substrate to prevent the element damages caused by static electricity.
As shown in FIG. 5, gate wire terminal portions 34's are formed in either end side of the gate wires 31a's, and likewise, data wire terminal portions 35's are formed in either end side of the data wires 32a's in the active matrix substrate. Conventionally, the gate wire terminal portions 34's and the data wire terminal portions 35's are extended to cause a short-circuit with a single ring short-circuit wire 36 provided along the periphery of the dielectric substrate 30 to release the static electricity.
However, the ring short-circuit wire 36 is cut off together with the peripheral portion of the dielectric substrate 30 at a cutting line 37 (denoted by an alternate long and short dash line) before a display module is installed into an assembled display panel, the result of which is illustrated in FIG. 6.
This is done so to conduct various kinds of electrical inspections on the display panel, correct revealed defects, and confirm the corrections before the display module is installed into the assembled display panel, which will be described below.
To be more specific, a simple electrical inspection in the first phase to check a disconnection of the gate wires 31a's and data wires 32a's is carried out while the display panel is assembled by disconnecting the ring short-circuit wire 36 at a portion where a short-circuit is made with the gate wire group 31 and at a portion where a short-circuit is made with the data wire group 32 to input a single signal into each wire.
On the contrary, to conduct a more detailed electrical inspection in the second phase to detect leakage defects among the gate wires and those among the data wires, different signals must be inputted into adjacent gate wires and adjacent data wires, respectively. However, if the dielectric substrate 30 still includes the ring short-circuit wire 36, only a single signal can be inputted respectively into the gate wire group 31 and data wire group 32, thereby disallowing the inspections in the second phase. Further, in case of a TFT-LCD (Liquid Crystal Display) which uses the Cs On Gate method as auxiliary capacity, if a single signal is inputted to the gate wire group 31 to drive the same, the same signal is inputted into adjacent gate wires 31a, thereby making the display almost impossible.
A method called "C conversion" is known as a correcting method of dot defects. In the C conversion, when there occurs leakage between a pixel electrode and a data wire 32a to which the pixel electrode is directly connected, an amount of leakage is increased by a laser beam or the like on purpose that the subject pixel electrode will receive the same signal its neighboring pixel electrodes are receiving to make the defective pixel less noticeable. However, the C conversion can not be adopted to correct leakage between a pixel electrode and a data wire 32a to which the pixel electrode is connected indirectly. Thus, to adopt the C conversion, different signals must be inputted into adjacent data wires 32a to find out which pixel electrode causes leakage with which data wire 32a in advance. In short, the ring short-circuit wire 36 must be cut off.
When correcting defects, especially leakage defects between the gate wire 31a and data wire 32a, it is important to specify the spot of the leakage. However, the dielectric substrate 30 including the ring short-circuit wire 36 allows only a simple electrical inspection, in which a single signal is inputted into the gate wire group 31 and data wire group 32, respectively. Thus, when there is more than one leakage spot, apparent leakage spots outnumber the actual leakage spots. For example, when there are four leakage spots, there are 16 intersections of the gate wires 31a's and data wires 32a's. Therefore, it is by no means easy to specify the actual leakage spots, and the ring short-circuit wire 36 must be cut off to make such spot specification easier.
Further, as shown in FIG. 6, line defects are conventionally corrected by providing sub-wires 38a and 38b to cause a short-circuit with a defective data wire 32a using a laser beam or the like. To confirm whether the line defects are corrected or not, the connection resistance between the sub-wires 38a and 38b is measured by measuring a resistance between sub-wire end portions 39a and 39b. To do so, however, the ring short-circuit wire 36 must be cut off completely.
As has been explained, with the above-structured conventional active matrix substrate, detailed electrical inspections are conducted and the revealed defects are corrected only after the ring short-circuit wire 36 is cut off. However, as previously mentioned, static electricity, which will cause the element damages, is generated during the steps of conducting electrical inspections of the display panel after the ring short-circuit wire 36 is cut off, correcting the revealed defects, transporting the display panel for the following step, and installing a driving module.
In addition, a probe must be applied to each of the terminal portions 34 of the gate wires 31a and the terminal portions 35 of the data wires 32a to detect leakage defects between the gate wires 31a's and data wires 32a's through the electrical inspections, correct the revealed defects, and measure the connection resistance between the sub-wires 38a and 38b to confirm the corrections after the ring short-circuit wire 36 is cut off. Thus, the inspections not only take considerable time and efforts, but also cost too much.